added support for HDL-64E S2.x models

I added support for HDL-64E S2.x Velodyne models. You can find a test file for HDL-64E S2.1 LIDAR together with the calibration files here: https://dl.dropboxusercontent.com/u/107064156/HDL-64E_S2.1.zip

The connecting issue's link: https://github.com/ros-drivers/velodyne/issues/11